1. Field of the Invention
The present invention relates to a pressure sensor, and more particularly, to a pressure sensor for sensing pressure in a high-temperature intense-vibration environment, such as combustion pressure of an engine.
2. Description of the Related Art
FIG. 7 schematically shows, in a sectional view, a conventional pressure sensor disclosed, for example, in Japanese Patent Laid-Open No. 4-76961. Referring to the drawing, the pressure sensor includes a cylindrical body casing 1 made of stainless steel or a like material. The body casing 1 has an opening portion 1a, on which is sealed a metal diaphragm 2 capable of deforming when subjected to pressure from the outside of the sensor. The metal diaphragm 2 is made of a stainless steel material with a thickness of approximately 100 to 150 .mu.m. A sealing member 4 is sealed to a portion of the inner surface 1b of the body casing 1 by a welding method or the like, and has a sealing portion 4a between that portion of the inner surface 1b and the main portion of the sealing member 4. The sealing member 4 cooperates with the body casing 1 and the metal diaphragm 2 to define a space within the body casing 1, in which space, a non-compressible medium 3 is sealed to maintain an air-tight condition in the space. A base 5 of the pressure sensor is formed of glass or a like material.
A semiconductor pressure-sensing unit 6 is disposed in the space and supported by the sealing member 4 through the base 5. When the metal diaphragm 2 deforms, the semiconductor pressure-sensing unit 6 is subjected to a corresponding pressure. The semiconductor pressure-sensing unit 6 has a semiconductor diaphragm 6a which receives such a pressure and undergoes a deformation in accordance with the received pressure. A strain gauge 7 is formed on one of the major surfaces of the semiconductor pressure-sensing unit 6 which opposes the metal diaphragm 2, and is capable of outputting an electrical signal in accordance with a deformation of the semiconductor diaphragm 6a. Leads 9 have upper portions 9a for receiving an electrical signal output by the strain gauge 7 and transmitted through wires 8, so as to lead the electrical signal to an external circuit (not shown). The strain gauge 7 has a circuit configuration shown in FIG. 8. As shown in FIG. 8, a plurality of strain-sensitive elements 7a, which are, for example, bridge-connected together, constitute the strain gauge 7.
The operation of the conventional pressure sensor will be described.
When a pressure A from the outside of the sensor acts on the metal diaphragm 2, as indicated by arrows in FIG. 7, the metal diaphragm 2 is accordingly deformed. Since an air-tight condition is maintained in the space within the body casing 1 by sealing the non-compressible medium 3 therein, the deformation of the metal diaphragm 2 causes a corresponding pressure to be applied to the semiconductor diaphragm 6a through the non-compressible medium 3, thereby causing a corresponding deformation of the semiconductor diaphragm 6a.
The strain gauge 7 senses the deformation of the semiconductor diaphragm 6a, and outputs an electrical signal of a magnitude corresponding to the magnitude of the deformation of the semiconductor diaphragm 6a, which signal is delivered to the external circuit.
The external circuit recognizes the magnitude of the pressure A on the basis of the signal output from the strain gauge 7.
When the conventional pressure sensor is subjected to intense vibration, disconnection may occur in the wires 8, or the wires 8 may be separated from the semiconductor pressure-sensing unit 6, thereby making it impossible to deliver electrical signals to the external circuit.